1. Technical Field of the Invention
The present invention relates to methods for cleaning works such as liquid crystal panels and relates to methods for manufacturing liquid crystal devices using the cleaning methods.
2. Description of the Related Art
When a liquid crystal device used as a display device is manufactured, after a panel is formed by bonding two substrates, liquid crystal is enclosed between the substrates by vacuum injection or the like. Next, after an inlet formed in the panel for injecting the liquid crystal therein is sealed, or after the panel is formed by cutting, the panel is cleaned so as to remove liquid crystal adhered to surfaces of the panel and is then connected to a flexible circuit substrate or the like by using an anisotropic conductive film.
As a cleaning liquid used for the cleaning described above, fluorinated cleaning liquids may be given as examples; however, since the fluorinated cleaning liquids cause destruction of the ozone layer, the usage thereof tends to be restricted or banned. Accordingly, in place of the fluorinated cleaning liquids, hydrocarbon-based cleaning liquids are gradually being used.
Hydrocarbon-based cleaning liquids can remove organic impurities; however, there is a problem in that the hydrocarbon-based liquids cannot sufficiently remove inorganic impurities. There may be a method for removing inorganic impurities by employing water cleaning in combination with cleaning using a hydrocarbon-based liquid; however, when water cleaning is employed, there are problems in that cost for a waste water treatment is high and in that a drying step takes a long period of time.
Accordingly, a method for cleaning both organic and inorganic impurities by using a hydrocarbon-based cleaning liquid containing a surfactant may be considered; however, when the cleaning liquid mentioned above is used, there is a problem in that a surfactant remaining on the liquid crystal panel after cleaning may have adverse influence in some cases.
In consideration of the problems described above, an object of the present invention is to provided a cleaning method in which both organic and inorganic impurities can be sufficiently removed from a work and in which a surfactant does not remain thereon, even when cleaning is performed by using a hydrocarbon-based cleaning liquid, and is to provide a method for manufacturing a liquid crystal device using the cleaning method described above.
In order to solve the problems described above, a cleaning method according to the present invention comprises a pre-cleaning step of performing at least immersion cleaning for a work by using a hydrocarbon-based cleaning liquid containing a surfactant; and a post-cleaning step of performing at least immersion cleaning for the work processed in the pre-cleaning step using a hydrocarbon-based cleaning liquid containing no surfactant; wherein, in the post-cleaning step, an operation of evacuating the inside of a cleaning bath and an operation of exposing the inside of the cleaning bath to air are repeated while the work is being immersed in the cleaning liquid.
In the present invention, after organic or inorganic impurities are removed by cleaning the work using the hydrocarbon-based cleaning liquid containing the surfactant (a pre-cleaning step), the work is cleaned by using the hydrocarbon-based cleaning liquid containing no surfactant, thereby cleaning out the hydrocarbon-based cleaning liquid containing the surfactant adhered to the work (post-cleaning step).
In addition, since in the post-cleaning step, the operation of evacuating the inside of the cleaning bath and the operation of exposing the inside thereof to air are repeatedly performed while the work is immersed in the cleaning liquid, during evacuation, bubbles grow and combine with each other in spaces of the liquid crystal panels and spaces between the liquid crystal panels so as to form larger bubbles and then escape from the spaces. Accordingly, the cleaning liquid smoothly infiltrates into the spaces, and hence, the hydrocarbon-based cleaning liquid containing the surfactant present in the spaces can be thoroughly replaced by the hydrocarbon-based cleaning liquid containing no surfactant. As a result, after the cleaning is performed, the organic and the inorganic impurities can be thoroughly removed from the work, and in addition, the surfactant contained in the hydrocarbon-based cleaning liquid used in the pre-cleaning step does not remain on the work.
In the present invention, the work is preferably brought out from the cleaning liquid while being inclined in at least one of the pre-cleaning step and the post-cleaning step. When the work is brought out in a manner as described above, a cleaning liquid, which does not flow out from the work in a normal position, flows out from the work. Consequently, an amount of the cleaning liquid adhered to the work brought out can be significantly decreased.
In the present invention, the work is preferably brought out from the cleaning liquid while being moved up and down in at least one of the pre-cleaning step and the post-cleaning step. When the work is brought out in a manner described above, a polluted cleaning liquid present in the spaces of the works and present therebetween can be thoroughly replaced by a cleaning liquid stored in the cleaning bath.
In the present invention, a step of drying the work is preferably performed between the pre-cleaning step and the post-cleaning step. When the step of drying is performed as described above, since the post-cleaning can be performed after the cleaning liquid present in the spaces of the works and spaces therebetween is removed, when the post-cleaning step is performed, the cleaning liquid smoothly infiltrates into the spaces of the works and spaces therebetween, whereby the post-cleaning can be satisfactory performed.
The cleaning method of the present invention can be applied to, for example, cleaning of liquid crystal panels each enclosing liquid crystal therein as the works. That is, when at least one substrate of a pair of substrates constituting the liquid crystal panel is a soda glass substrate, even though the soda glass substrate is inexpensive, there is a shortcoming in that alkali metals contained therein are precipitated on surfaces of the glass and then form the salts thereof. However, in the present invention, since the inorganic materials described above are cleaned out by the cleaning liquid containing a surfactant, according to the present invention, the problem of the glass substrate in that the salts composed of the alkali metals precipitated on the surfaces thereof cause corrosion can be solved.
The present invention is more effectively applied to the case in which cleaning is performed when a plurality of liquid crystal panels are placed adjacent to each other. In the present invention, since an evacuated state and a state at an atmospheric pressure are repeatedly performed while the liquid crystal panels are immersed in the cleaning liquid in the post-cleaning step, during the evacuated state, bubbles grow and combine with each other so as to for larger bubbles and escape from the spaces. Consequently, since the cleaning liquid smoothly infiltrates into the spaces of the liquid crystal panels and spaces therebetween, the cleaning liquid containing the surfactant present in the spaces of the liquid crystal panels and spaces therebetween can be thoroughly replaced by the cleaning liquid containing no surfactant. As a result, after the cleaning is performed, organic and inorganic impurities can be thoroughly removed from the liquid crystal panels, and in addition, the surfactant contained in the cleaning liquid used in the pre-cleaning step does not remain thereon.